text: function getUndoList(subject,callback) {
      let url = "/undolist?subject=" + subject;
      
      fetch(url,{
          method:"GET"
      }).then((res)=>{
          res.text().then((data)=>{
              callback(JSON.parse(data))
          });
      });
  }
  
  function showData(students,id){
      students.forEach((student) => {
          let html = `
              <tr>
                  <td>${student.id}</td>
                  <td>${student.name}</td>
              </tr>
          `;
          document.getElementById(id).innerHTML += html;
      });
  }
  
  getUndoList("HTML",(data)=>{
      showData(data,"undoHtml");
  });
  
  getUndoList("SQL",(data)=>{
      showData(data,"undoSql");
  });
  
  getUndoList("Python",(data)=>{
      showData(data,"undoPython");
  });
  
  getUndoList("Cyol",(data)=>{
      showData(data,"undoCyol");
  });